Passive and active sensors for ultrasound tracking

ABSTRACT

A system performs a medical procedure in a region of interest of a patient. The system includes an interventional medical device insertable into the region of interest, and a sensor attached to a portion of the interventional device, the sensor being configured to convert an ultrasonic wave from an ultrasound imaging probe to a corresponding electrical radio frequency (RF) signal. The corresponding RF signal is received by a wireless receiver outside the region of interest, enabling determination of a location of the sensor within the region of interest.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation application of U.S. application Ser.No. 16/468,022, filed on Jun. 10, 2019, which is a U.S. National Phaseapplication under 35 U.S.C. § 371 of International Application No.PCT/EP2017/081943, filed Dec. 8, 2017, which claims the benefit of U.S.Provisional Application No. 62/433,051, filed on Dec. 12, 2016. Theseapplications are hereby incorporated by reference herein.

BACKGROUND

Location tracking of medical devices used in-situ on a patient enablesless invasive medical procedures to be carried out. By way of example,ultrasound-guided medical procedures enable the location of certainmedical devices relative to a position of interest in a patient.

In certain ultrasound based medical device tracking, electrical wiresrunning from the tip to the handle of the medical device transmitsignals to a console/workstation for data analysis.

Among other drawbacks, the connection of the medical instrument to theconsole/workstation by cables complicates clinical workflow, andintroduces undesirable cable management. As a result, the clinicalworkflow is often impeded because of the presence of cables connectingthe medical device to the console. This not only makes it cumbersome forthe clinician to perform the procedure, but also limits the marketacceptance of such known cable-connected devices and systems.

Accordingly, it is desirable to provide an apparatus, systems, methods,and computer-readable storage media for determining a position of amedical instrument, in-situ, which overcomes at least the short-comingsof the above-described known devices.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be more readily understood from the detaileddescription of representative embodiments presented below considered inconjunction with the accompanying drawings, as follows.

FIG. 1A is a conceptual diagram depicting two-way ultrasound signaltransmission, in accordance with a representative embodiment.

FIG. 1B is a conceptual diagram depicting one-way ultrasound signaltransmission, in accordance with a representative embodiment.

FIG. 2 is a schematic block diagram showing an ultrasound system, inaccordance with a representative embodiment.

FIG. 3A is a simplified schematic block diagram showing a medicaldevice, in accordance with a representative embodiment.

FIG. 3B is a simplified schematic diagram showing a medical device, inaccordance with another illustrative embodiment of the presentinvention.

FIG. 4A is a conceptual diagram depicting a frame scan using a pluralityof ultrasound beams.

FIG. 4B shows the relative timing of frame trigger signals, line triggersignals, and a received sensor signal of a medical device in accordancewith a representative embodiment.

FIG. 5 is a conceptual diagram depicting a passive ultrasound transducerthat harvests energy, according to a representative embodiment.

FIG. 6A is a conceptual diagram depicting a passive ultrasound sensorthat receives a continuously broadcast, lower frequency RF signals froman RF transmitter via an external antenna, according to a representativeembodiment.

FIG. 6B is a conceptual diagram depicting a capacitive micromachinedultrasonic transducer (CMUT) that may be incorporated as a passiveultrasound sensor, according to a representative embodiment.

FIG. 6C is a conceptual diagram depicting a passive ultrasound sensorthat receives a continuously broadcast external RF signal at firstfundamental frequency, and reflects a harmonic signal at secondfundamental frequency, according to a representative embodiment.

FIG. 7 is a conceptual diagram depicting an active sensor that harvestsenergy to send an RF signal for active retransmission, according to arepresentative embodiment.

FIG. 8 is a conceptual diagram depicting an active sensor that sends anRF signal for active retransmission via wires, according to arepresentative embodiment.

DETAILED DESCRIPTION

The present teachings are described hereinafter with reference to theaccompanying drawings, in which representative embodiments are shown.The present teachings may, however, be embodied in different forms andshould not be construed as limited to the embodiments set forth herein.Rather, these embodiments are provided as teaching examples.

Generally, according to various embodiments, is to be understood thatthe terminology used herein is for purposes of describing particularembodiments only, and is not intended to be limiting. Any defined termsare in addition to the technical and scientific meanings of the definedterms as commonly understood and accepted in the technical field of thepresent teachings.

As used in the specification and appended claims, the terms “a”, “an”and “the” include both singular and plural referents, unless the contextclearly dictates otherwise. Thus, for example, “a device” includes onedevice and plural devices.

Unless otherwise noted, when an element or component is said to be“connected to,” “coupled to” another element or component, it will beunderstood that the element or component can be directly connected,directly coupled to the other element or component, or, interveningelements or components may be present. That is, these and similar termsencompass cases where one or more intermediate elements or componentsmay be employed to connect two elements or components. However, when anelement or component is said to be “directly connected” to anotherelement or component, this encompasses only cases where the two elementsor components are connected to each other without any intermediate orintervening elements or components.

Also, it will be understood that, in addition to their ordinarymeanings, the terms “substantial” or “substantially’ mean to withinacceptable limits or degree to one having ordinary skill in the art. Forexample, “substantially cancelled” means that one of ordinary skill inthe art would consider the cancellation to be acceptable. Likewise, inaddition to its ordinary meaning, the term “approximately” means towithin an acceptable limit or amount to one having ordinary skill in theart. For example, “approximately the same” means that one of ordinaryskill in the art would consider the items being compared to be the same.

Directional terms/phrases and relative terms/phrases may be used todescribe the various elements' relationships to one another, asillustrated in the accompanying drawings. These terms/phrases areintended to encompass different orientations of the device and/orelements in addition to the orientation depicted in the drawings.

Like numbered elements in these figures are either equivalent elementsor perform the same function. Elements which have been discussedpreviously will not necessarily be discussed in later figures if thefunction is equivalent.

Initially, it is noted that medical images may include 2D or 3D imagessuch as those obtained using an ultrasound probe, and a position of amedical instrument relative to an image frame of ultrasound signals fromthe ultrasound probe.

In accordance with a representative embodiment, an apparatus forperforming a medical procedure is disclosed. The apparatus comprises; asensor adapted to convert an ultrasonic signal incident thereon into anelectrical signal; and a wireless transceiver configured to receive theelectrical signal from the sensor, and to transmit the electrical signalto a wireless receiver remote from the apparatus.

In accordance with another representative embodiment, an ultrasoundsystem, comprises: an ultrasound probe adapted to insonify a region ofinterest; an apparatus configured to perform a medical procedure, theapparatus comprising: a sensor adapted to convert an ultrasonic signalincident thereon into an electrical signal; and a first wirelesstransceiver configured to transmit the electrical signal; and a controlunit remote from the ultrasound probe and apparatus. The control unit isadapted to provide an image from the ultrasound probe. The control unitcomprises: a second wireless transceiver configured to receive theelectrical signal from the first wireless transceiver, and a processoradapted to overlay the position of the apparatus on the image.

FIGS. 1A and 1B offer, by way of an illustrative and non-limitativeexample, a comparison between two-way beamforming (FIG. 1A) and one-wayonly beamforming (FIG. 1B).

Turning to FIG. 1A, representative of two-way beamforming shows animaging array 102 of N elements 104 issuing ultrasound signals thatimpinge on a reflector 106. Since the ultrasound waves go out and back(from the imaging array to the reflectors and back to the imagingarray), this beamforming is “two-way” or “round-trip” beamforming. Onreceiving (of the ultrasound that has reflected back), beamformingdetermines the reflectivity of the reflector 106 and the position of thereflector relative to the array 102. The array 102 sends out anultrasound beam 108 that is reflected from the reflector 106 and returnsto all elements 104 of the array 102. The flight of the beam is over adistance r(P)+d(i,P) for element i. Each element 104 measurescontinually the amplitude of the return ultrasound. For each element104, the time until a maximum of that measurement, i.e., the “round-triptime of flight,” is indicative of the total flight distance. Since ther(P) leg of the flight is constant, the return flight distance d(i,P) isdetermined. From these measurements, the relative position of thereflector 106 is computed geometrically. As to the reflectivity of thereflector 106, it can be indicated by summing the maxima over all i(i.e., over all elements 104). Notably, beamforming, a geometricalcomputation, not only takes place in receive mode but also in transmitmode. As such a beamformer (e.g., beamformer 210 described in connectionwith FIG. 2 ) in transmit mode sends properly delayed signals to all theelements 104 (and generates the frame and line trigger signals), and inreceive mode properly delays and sums the signals from the individualelements 104.

When imaging tissue, there may be many reflectors with varyingreflection magnitudes, respectively. To find tissue reflection intensityat a particular location, the geometrical element delays for thatlocation are calculated and the shifted signals are summed. These delaysvary dynamically in time as the whole imaging frame is beingconstructed, in a process referred to as dynamic receive beamforming.For tracking of the instrument, data may be recorded with a sensor atthe device location, and the timing of frame and line triggers may alsobe recorded.

Turning to FIG. 1B, one-way only (receive) beamforming is depicted.Notably, as the name implies, in one-way beamforming there is echo, butit is not used. Instead, an ultrasound transmitter 110 emits anultrasound beam 112, which is incident on each element 104 of the array102. The flight here, in contrast to the two-way beamforming case, isover the distance d (i,P). The time from emission of the ultrasound beam112 until the maximum amplitude reading at an element 104 determines thevalue d (i,P) for that element i. Thus, the position of the ultrasoundtransmitter 110 can be derived geometrically, and the reflectivitycalculated by summing the maximum amplitude readings.

Although one-way beamforming is implementable in the time domain viadelay logic, as discussed hereinabove, it can also be implemented in thefrequency domain by well-known Fourier beamforming algorithms.

As will become clearer as the present description continues, two-waybeamforming is used to gather images on a frame-by-frame basis; andone-way beamforming is used to determine the location of a sensordisposed at a known position on a medical device (sometimes referred togenerically as an apparatus). For example, the sensor could be attachedat or near (e.g., about 1 mm away from) the tip (or distal end) of aneedle or other medical device.

FIG. 2 is a simplified schematic block diagram showing an ultrasoundsystem 200, in accordance with a representative embodiment of thepresent invention. The ultrasound system 200 comprises a number ofcomponents, the functions of which are described more fully below.

The ultrasound system comprises a control unit 201, which is connectedto a display 203, and a user interface 204. The control unit 201comprises a processor 205, which is connected to a memory 206, and inputoutput (I/O) circuitry 207. The control unit 201 further comprises aclock (CLK) 208 (sometimes referred to below as a first clock), whichprovides clock signals, to the I/O circuitry for distribution to and usein the ultrasound system 200, as described more fully below. As willbecome clearer as the present description continues, the clock 208 issubstantially synchronized with a clock (not shown) of a medical device214 to ensure substantial simultaneity of frame and trigger signalsprovided by the control unit 201 during a scan.

The control unit 201 also comprises a wireless transceiver 209, which isadapted to connect to various components of the ultrasound system 200,such as a wireless network 202, and others as described more fullybelow.

Finally, the control unit 201 comprises a beamformer 210. The beamformer210 is adapted to receive signals from an ultrasound imaging probe 211.As described more fully below, the ultrasound imaging probe 211 isadapted to scan the region of interest 212, and provides images on aframe-by-frame basis.

The ultrasound system 200 also comprises the medical device 214, whichcomprises a sensor 215 (see FIGS. 3 and 4 for more detail) disposed ator near (a known distance from) a distal end 216 of the medical device214. The distal end 216 is disposed at a target location in the regionof interest 212.

As described more fully below, the sensor 215 is adapted to convertultrasound beams provided by the ultrasound imaging probe 211 intoelectrical signals, and to provide either the raw data from the sensor215, or partially or completely processed data (e.g., calculated sensorlocation) from the sensor 215, to the control unit 201 via the wirelesstransceiver, either directly or indirectly (e.g., via a transmitter orrepeater located in a proximal end of the medical device 214). Thesedata, depending on their degree of processing, are either used by thecontrol unit 201 to determine the location of the distal end 216 of themedical device 214, or provide to the control unit 201 the location ofthe distal end 216 of the medical device 214.

As will become clearer as the present description continues, the controlunit 201 is illustratively a computer system, which comprises a set ofinstructions that can be executed to cause the control unit 201 toperform any one or more of the methods or computer based functionsdisclosed herein. The control unit 201 may operate as a standalonedevice (e.g., as the computer of a stand-alone ultrasound system), ormay be connected, for example, using a wireless network 202, to othercomputer systems or peripheral devices. Generally, connections to thewireless network 202 are made using a hardware interface, which isgenerally a component of I/O circuitry 207, which is described below.

In accordance with a representative embodiment, the display 203 is anoutput device and/or a graphical user interface adapted for displayingimages or data. A display may output visual, audio, and or tactile data.The display 203 may be, but is not limited to: a computer monitor, atelevision screen, a touch screen, tactile electronic display, Braillescreen, Cathode ray tube (CRT), Storage tube, Bistable display,Electronic paper, Vector display, Flat panel display, Vacuum fluorescentdisplay (VF), Light-emitting diode (LED) displays, Electroluminescentdisplay (ELD), Plasma display panels (PDP), Liquid crystal display(LCD), Organic light-emitting diode displays (OLED), a projector, andHead-mounted display, for example.

The user interface 204 allows a clinician or other operator to interactwith the control unit 201, and thereby with the ultrasound system 200.The user interface 204 may provide information or data to the operatorand/or receive information or data from the clinician or other operator,and may enable input from the clinician or other operator to be receivedby the control unit 201 and may provide output to the user from thecontrol unit 201. In other words, the user interface 204 may allow theclinician or other operator to control or manipulate the control unit,and may allow the control unit 201 to indicate the effects of thecontrol or manipulation by the clinician or other operator. The displayof data or information on the display 203 or graphical user interface isan example of providing information to an operator. The receiving ofdata through a touch screen, keyboard, mouse, trackball, touchpad,pointing stick, graphics tablet, joystick, gamepad, webcam, headset,gear sticks, steering wheel, wired glove, wireless remote control, andaccelerometer are all examples of user interface components which enablethe receiving of information or data from a user.

The user interface 204, like the display 203 are illustratively coupledto the control unit 201 via a hardware interface (not shown) and the I/Ocircuitry 207 as would be appreciated by those skilled in the art. Thehardware interface enables the processor 205 to interact with variouscomponents of the ultrasound system 200, as well as control an externalcomputing device (not shown) and/or apparatus. The hardware interfacemay allow the processor 205 to send control signals or instructions tovarious components of the ultrasound system 200, as well as an externalcomputing device and/or apparatus. The hardware interface may alsoenable the processor 205 to exchange data with various components of theultrasound system, as well as with an external computing device and/orapparatus. Examples of a hardware interface include, but are not limitedto: a universal serial bus, IEEE 1394 port, parallel port, IEEE 1284port, serial port, RS-232 port, IEEE-488 port, Bluetooth connection,Wireless local area network connection, TCP/IP connection, Ethernetconnection, control voltage interface, MIDI interface, analog inputinterface, and digital input interface.

In a networked deployment, the control unit 201 may operate in thecapacity of a server or as a client user computer in a server-clientuser network environment, or as a peer control unit in a peer-to-peer(or distributed) network environment. The control unit 201 can also beimplemented as or incorporated into various devices, such as astationary computer, a mobile computer, a personal computer (PC), alaptop computer, a tablet computer, a wireless smart phone, a set-topbox (STB), a personal digital assistant (PDA), a global positioningsatellite (GPS) device, a communications device, a control system, acamera, a web appliance, a network router, switch or bridge, or anyother machine capable of executing a set of instructions (sequential orotherwise) that specify actions to be taken by that machine. The controlunit 201 can be incorporated as or in a particular device that in turnis in an integrated system that includes additional devices. In arepresentative embodiment, the control unit 201 can be implemented usingelectronic devices that provide voice, video or data communication.Further, while a single control unit 201 is illustrated, the term“system” shall also be taken to include any collection of systems orsub-systems that individually or jointly execute a set, or multiplesets, of instructions to perform one or more computer functions.

The processor 205 for the control unit 201 is tangible andnon-transitory. As used herein, the term “non-transitory” is to beinterpreted not as an eternal characteristic of a state, but as acharacteristic of a state that will last for a period of time. The term“non-transitory” specifically disavows fleeting characteristics such ascharacteristics of a particular propagating carrier wave or signal orother forms that exist only transitorily in any place at any time.

The processor 205 is an article of manufacture and/or a machinecomponent. As described more fully below, the processor 205 isconfigured to execute software instructions in order to performfunctions as described in the various representative embodiments herein.The processor 205 may be a general purpose processor or may be part ofan application specific integrated circuit (ASIC). The processor 205 mayalso be a microprocessor, a microcomputer, a processor chip, acontroller, a microcontroller, a digital signal processor (DSP), a statemachine, or a programmable logic device. The processor 205 may also be alogical circuit, including a programmable logic device (PLD) such as aprogrammable gate array (PGA), a field programmable gate array (FPGA),or another type of circuit that includes discrete gate and/or transistorlogic. The processor 205 may be a central processing unit (CPU), agraphics processing unit (GPU), or both. Additionally, the processor 205may include multiple processors, parallel processors, or both. Multipleprocessors may be included in, or coupled to, a single device ormultiple devices of the ultrasound system 200.

The memory 206 is an article of manufacture and/or machine component,and is a computer-readable medium from which data and executableinstructions can be read by a computer. The memory 206 may include oneor more of random access memory (RAM), read only memory (ROM), flashmemory, electrically programmable read only memory (EPROM), electricallyerasable programmable read-only memory (EEPROM), registers, a hard disk,a removable disk, tape, compact disk read only memory (CD-ROM), digitalversatile disk (DVD), floppy disk, blu-ray disk, or any other form ofstorage medium known in the art. Memories may be volatile ornon-volatile, secure and/or encrypted, unsecure and/or unencrypted.

Generally, the memory 206 comprises a tangible storage medium that canstore data and executable instructions, and are non-transitory duringthe time instructions are stored therein. Further, the instructionsstored in memory 206, when executed by the processor 205, can be used toperform one or more of the methods and processes as described herein. Ina particular embodiment, the instructions may reside completely, or atleast partially, within the memory 206. Notably, the instructions mayreside within the processor 205 during execution by the control unit201.

In accordance with a representative embodiment described below inconnection with FIGS. 3A-4B, the position of the sensor 215 isdetermined by the medical device 214 and transmitted to the control unit201 via the wireless transceiver 209. Using the position of the sensor215 provided, the processor 205 executes instructions stored in memory206 to overlay the position of the sensor 215 an image frame, and thusthe distal end 216 of the medical device 214 relative to the image ofeach frame. In another representative embodiment, the instructionsstored in memory 206 are executed by the processor 205 to determine aposition of the sensor 215 in an image frame, and to overlay theposition of the sensor 215, and thus the distal end 216 of the medicaldevice 214 relative to the image of each frame. One illustrative methodof determining the position of the distal end 216, for whichinstructions are stored in memory 206 is described below in connectionwith FIGS. 4A and 4B.

Alternatively, in accordance with a representative embodiment, and asalluded to above, dedicated hardware implementations, such asapplication-specific integrated circuits (ASICs), programmable logicarrays and other hardware components, can be constructed to implementone or more of the methods and processes described herein. One or morerepresentative embodiments described herein may implement functionsusing two or more specific interconnected hardware modules or deviceswith related control and data signals that can be communicated betweenand through the modules. Accordingly, the present disclosure encompassessoftware, firmware, and hardware implementations. Nothing in the presentapplication should be interpreted as being implemented or implementablesolely with software and not hardware such as a tangible non-transitoryprocessor and/or memory.

In accordance with various embodiments of the present disclosure, themethods described herein may be implemented using a hardware-basedcontrol unit 201 that executes software programs. Further, in arepresentative embodiment, implementations can include distributedprocessing, component/object distributed processing, and parallelprocessing. Virtual computer system processing can be constructed toimplement one or more of the methods or functionality as describedherein, and the processor 205 described herein may be used to support avirtual processing environment.

The present teachings contemplate a computer-readable medium thatincludes instructions, or receives and executes instructions responsiveto a propagated signal; so that a device connected to the wirelessnetwork 202 can communicate voice, video or data over the wirelessnetwork 202. Further, the instructions may be transmitted or receivedover the wireless network 202 via a network interface device (notshown).

The wireless transceiver 209 is contemplated to be a radio frequency(RF) transceiver, or an optoelectronic transceiver. As described morefully below, the medical device 214 comprises a transceiver adapted tocommunicate with the wireless transceiver, and thus may be an RFtransceiver or an optoelectronic transceiver, depending on thecomponents of the wireless transceiver. The wireless transceiver 209thus comprises at least an antenna, multiplexing/demultiplexingcomponents, amplifiers and filters as needed to transmit and receivedata to and from the medical device 214.

The I/O circuitry 207 receives inputs from various components of theultrasound system 200, and provides output to and receives inputs fromthe processor 205, as is described more fully below. I/O circuitry 207controls communication to elements and devices external to the controlunit 201. The I/O circuitry 207 acts as an interface including necessarylogic to interpret input and output signals or data to/from theprocessor 205. The I/O circuitry 207 is configured to receive theacquired live images from the beamformer 210, for example, via a wiredor wireless connection. The I/O circuitry 207 is also configured toreceive data from the medical device 214. As described more fully below,the I/O circuitry 207 provides these data to the processor 205 toultimately superpose the location of the distal end 216 of the medicaldevice 214 in a particular image frame.

Broadly, in operation, based on input from the user interface 204provided to the processor 205 by the I/O circuitry 207, the processor205 initiates a scan by the ultrasound imaging probe 211. The scanlaunches ultrasound waves across the region of interest 212. Theultrasound waves are used to form an image of a frame by the beamformer210; and to determine the location of the sensor 215 of the medicaldevice 214. As can be appreciated, the image is formed from a two-wayultrasound transmission sequence, with images of the region of interestbeing formed by the transmission and reflection of sub-beams byplurality of transducers. By contrast, these sub-beams are incident onthe sensor 215, which converts the ultrasound signals into electricalsignals in a one-way ultrasound method. As described below in connectionwith FIGS. 4A and 4B, based on frame and line trigger signals generatedin beamformer 210 and via the wireless transceiver 209 provided to themedical device 214, the location of the sensor 215 is determined.

While images in the region of interest 212 are being garnered by theultrasound imaging probe 211, one-way data is garnered by the sensor215. As noted above, and as described more fully below, these data maycomprise raw data, partially processed data, or fully processed data.Depending on the degree of processing, these data can be provided to theprocessor 205 for executing instructions stored in the memory 206 todetermine the position of the sensor 215 in the coordinate system ofultrasound images from the beamformer 210; or may include the determinedposition of the sensor 215 in the coordinate system which is used by theprocessor when executing instructions stored in the memory 206 tooverlay the position of the sensor 215 on the ultrasound image in thecoordinate system thereof. To this end, the beamformer 210 processes thebeamformed signal for display as an image of a frame. The output fromthe beamformer 210 can be provided to the processor 205. The data fromthe sensor 215 may be raw data, in which case the processor 205 executesinstructions in the memory 206 to determine the position of the sensor215 in the coordinate system of the image; or the data from the sensor215 may be processed by the medical device to determine the location ofthe sensor 215 in the coordinate system of the image. Either way, theprocessor 205 is configured to overlay the position of the sensor 215 ina particular frame on the image from the beamformer 210 from that frame.A composite image 218, comprising the image of the frame from theultrasound imaging probe 211 and the superposed position 219 of thesensor 215 in that frame is provided on the display 203 providingreal-time feedback to a clinician of the position of the distal end 216of the medical device 214 relative to the region of interest 212. As canbe appreciated, the superposing of the position of the sensor 215 isrepeated for each frame to enable complete real-time in-situsuperposition of the position of the sensor 215 relative to thecomposite image 218 of the particular frame.

FIG. 3A is a simplified schematic block diagram showing a medical device300, in accordance with a representative embodiment. Many details of themedical devices described above in connection with FIGS. 1A-2 are commonto the details of medical device 300, and may not be repeated in thedescription of the medical device 300.

The medical device 300 is contemplated to be any one of a number ofmedical devices where the location of a distal end relative to aposition in a region of interest, including but not limited to a needle,such as a biopsy or therapeutic needle, or a medical instrument, such asa laparoscope, or a scalpel, is desired. It is emphasized that thelisted medical devices are merely illustrative, and other medicaldevices that benefit a clinician through the determination of theirdistal ends are contemplated.

Turning to FIG. 3A, the medical device 300 comprises a sensor 302disposed at or near (a known distance from) a distal end 301. Asdescribed above, the sensor 302 is an ultrasonic sensor adapted toconvert ultrasonic (mechanical) waves incident thereon into electricalsignals. In a representative embodiment, the sensor comprises apiezoelectric element, such as a thin film piezoelectric material, or apiezoceramic material. Upon incidence of an ultrasound signal, thesensor effects the conversion, and electrodes (not shown) connected tothe sensor 302 transmit the electrical signal through electrical oroptical conductors 303 to a hub 304. The hub 304 may be for example, thehandle of the medical device 300, which is disposed at the proximal endof the medical device 300.

After processing of the electrical signal from the sensor 302, asdescribed above and below, a wireless transceiver 312 transmits theprocessed electrical signal to a console (e.g., control unit 201) remotefrom the medical device 300. As noted above, depending on the type ofwireless transceiver at the console (e.g., wireless transceiver 209 ofcontrol unit 201), the wireless transceiver 312 may be an RF transceiveror an optoelectronic transceiver, for example, adapted to transmit andreceive data from the console, although other transceivers may beincorporated without departing from the scope of the present teachings.

By way of example, the wireless connection between the wirelesstransceiver 312 and the wireless transceiver at the console may beconfigured to operate under a known wireless protocol, including, butnot limited to Zigbee, Bluetooth, or Wi-Fi, and include the necessarycomponents to effect the layer structure of the protocol. Alternatively,the wireless connection may be implemented using a proprietary protocol.

Moreover, an optical link may be used to effect the wireless connection.Just by way of example, in accordance with a representative embodiment,two narrow band light emitters (i.e. a red and a green LED) may be usedto effect the wireless connection. Illustratively, a 128 bit pulsesequence can be created with a red flash representing a “0”, and a greenflash representing a “1” to transmit a 128 bit number. Error correctingcoding such as Reed-Solomon can be used to have more robusttransmission.

In the presently described representative embodiment, the medical device300 comprises a signal conditioning module 305, a processor 306, and amemory 307. Notably, the processor 306 and memory 307 may comprise thesame or similar structure and composition of the processor 205 andmemory 206 described above.

The medical device 300 also comprises a clock 308 (sometimes referred toas a second clock), which is substantially synchronized with the clockof the console (e.g., clock 208 depicted in FIG. 2 ). As described morefully below in connection with FIGS. 4A-4B, the timing of frame and linetrigger signals received from the console/control unit, are used todetermine the location of the sensor 302. As such, the substantialsynchronization of the clock 308 and the remote clock (e.g., clock 208)is useful in ensuring the determination of the timing, and thereby thelocation, of the sensor 302 relative to a scanned image of a particularframe.

As shown in FIG. 3B, the signal conditioning module 305 comprises anamplifier 309, a filter 310, and a digitizer 311. The amplifier 309 andfilter 310 may be one of a number of known components useful inamplifying and filtering an electrical signal to provide a desiredminimum signal to noise ratio (SNR). The digitizer 311 may be a knowndigitizer, such as an analog to digital (A/D) converter commonly used inRF or optical communications, depending on the chosen medium fortransmission between the medical device 300 and the remote console.

In accordance with a representative embodiment, the amplifier 309 may beoptimized for the acoustic sensor 302 and include features such ascharge amplification and balanced inputs with high common mode signalrejection, or if the sensor is optoacoustic in nature, include forexample a photo-transistor. The filter 310 may be a simple analogbandpass filter, an analog envelope detector with RF carrier frequencydemodulation, or may contain a nonlinear resonant structure that ishighly sensitive to specific waveform patterns. The digitizer 311 maysample at rates suitable for raw RF signals, or a lower rate sufficientfor proper RF envelope sampling. To optimize dynamic range, nonlinearquantization steps (such as LOG scale) may be used, and/or the digitizerreference voltage may be based on recently measured signal amplitudes orchange in time (TGC).

An input signal from the sensor 302 is received through the electricalor optical conductors 303 at the amplifier 309, where it is amplified toa suitable level, and transmitted to the filter 310. After receipt fromthe filter 310, the signal is digitized by the digitizer 311, andprovided to the processor 306 (see FIG. 3A).

The memory 307 comprises a tangible storage medium that can store dataand executable instructions, and are non-transitory during the timeinstructions are stored therein. The instructions stored in memory 307are executed by the processor 306 to determine a position of the sensor302 in each image frame. One illustrative method of determining theposition of the distal end 301, for which instructions are stored inmemory 307 is described below in connection with FIGS. 4A and 4B.

As described above, the electrical signal transmitted from the wirelesstransceiver 312 may be partially or completely processed prior totransmission to a remote wireless transceiver (e.g., wirelesstransceiver 209 of control unit 201). In the presently describedembodiment, the signal from the sensor 302 is used to determine thelocation of the distal end 301. This location is then transmitted to theremote control unit, where it is used to overlay the position of thedistal end 301 real time, as noted above.

One method for determining the location of the distal end comprisescollecting/storing the signal from the sensor 302 over the duration of acomplete frame, then find the time at clock 308 where maximum signal isreceived (again, the clock 308 is synchronized using the frame and linetriggers that are wirelessly received). As the beam transmit parametersare known, this clock time can then be used to either mathematicallycalculate the position or find the position in a lookup table stored inmemory 307, for example. The calculation/lookup could take place in themedical device 300, and coordinates transmitted to the remotely locatedcontrol unit 201, or the clock time from clock 308 could be transmittedand calculation/lookup performed in control unit 201.

In an alternative embodiment, the processor 306, clock 308, and memory307 are not provided in the medical device 300, and only partiallyprocessed data is transmitted by the wireless transceiver 312 to thecontrol unit. The sensor signal is now transmitted (e.g., continuously)through a channel that has a fixed and known latency. In the presentexample, partially processed data comprises the amplified and filteredsignal that can be either kept analog or optionally can be digitized andprovided at the output of the signal conditioning module 305. These dataare provided to the wireless transceiver 312, and transmitted to theremote console/control unit. As described above, in this latterembodiment, the control unit comprises a processor (e.g., processor 205)and memory (e.g., memory 206) useful in determining the position of thesensor 302 and thus distal portion; and is adapted to overlay thedetermined position on an image from a scan real-time. The timing of thedetected maximum sensor signal is known due to the fixed/known latencyof the wireless transmit channel, and line and frame trigger signals areavailable from the beamformer (e.g., beamformer 210) in transmit mode.

Notably, as part of processing, the signal from the sensor 302 may beclipped to include only the relevant parts of the signal (e.g., in andaround the maximum signal intensity location as described below inconnection with FIGS. 4A and 4B) for each frame. Furthermore, the signalof only the ultrasound beam incident on the sensor 302 with the maximumsignal may be transmitted (along with other information such as timingand encoding parameters). Beneficially, these methods are aimed atreducing the size of the data packet before transmission from thewireless transceiver 312, thereby allowing for easier transmission fromthe medical device 300 to the console.

FIG. 4A is a conceptual diagram depicting a frame scan 400 using aplurality of ultrasound beams of an ultrasound system of arepresentative embodiment. FIG. 4B shows the relative timing of frametrigger signals, line trigger signals, and a received sensor signal of amedical device in accordance with a representative embodiment. Manydetails of the medical devices described above in connection with FIGS.1A-3B are common to the details of the conceptual diagram and timingdiagram of FIGS. 4A-4B, and may not be repeated in their description.

Turning to FIG. 4A, medical device 300 having sensor 302 at or near (aknown distance from) a distal end is provided in proximity in-situ to aregion of interest in a body, for example. A plurality of ultrasoundtransducers 4011-401N each generates respective ultrasound beams (beams1-beam N) in a scan across the region of interest. As shown in FIG. 4B,frame trigger (e.g., First Frame), which is provided at the beginning ofa scan, results in scanning over the region of interest to provide animage frame. As is known, the scanning is sequential from ultrasoundtransducer 4011 through 401N, and at the next frame, the sequence isrepeated to generate the next image frame (Frame 2). Moreover, eachultrasound beam (beams 1-beam N) is triggered by a respective linetrigger, with each successive beam being terminated at the reception ofthe next line trigger.

As depicted in FIGS. 4A and 4B, a first frame scan (Frame 1) begins witha frame trigger, with the first ultrasound transducer 4011 being excitedat the first line trigger (Line 1). Next, the second ultrasoundtransducer 402 is excited at the second line trigger (Line 2). As notedabove this sequence continues until the end of the first frame at whichpoint the second frame scan (Frame 2) begins with the second frametrigger, which coincides with the first line trigger of the second/nextframe. The sequence begins anew by the exciting of the first ultrasoundtransducer 4011 at the first line trigger (Line 1); followed by thesecond ultrasound transducer 402 at the second line trigger (not shown)of the second frame; and so forth until the termination of the secondframe.

As can be seen in FIGS. 4A and 4B, a signal is received at the sensor302 at a time coinciding with the line trigger n+1, with a maximumamplitude being received at a time Δt along the line n+1. As describedpresently, this signal is used to determine the location of the sensor302 relative to the first frame, and is superposed on the image of theframe, and thereby at a particular coordinate (x,y) of the coordinatesystem of the first frame image (e.g., composite image 218, comprisingthe image of the frame from the ultrasound imaging probe 211 and thesuperposed position 219 of the sensor). That is, for example, whenperforming 2D imaging, all sensor data is collected for one frame,timing of maximum sensor signal over that frame is determined, thesensor position is calculated after the last beam of the frame, and thenthe frame is displayed and the sensor location is drawn on the frame. In3D imaging, all data for the volume is first collected, then that volumeis rendered and the sensor position is annotated in that volume.

In a first representative embodiment, and as noted above, the positionof the sensor in the coordinate system of the first frame is determinedat the processor of the console/control unit (e.g., processor 205). Insuch an embodiment, the medical device 300 transmits the data from thesensor to the console/control unit that is remotely located. These dataare provided to the processor (e.g., processor 205), and theinstructions stored in memory (e.g., memory 206) are executed by theprocessor to determine a position of the sensor 302 in an image frame,and to overlay the position of the sensor 302, and thus the distal endof the medical device 300 relative to the image of the first frame.

As noted above the first and second clocks 208, 308 are substantiallysynchronized with respect to each other. The first and second clocks208, 308 can be one-time synchronized, synchronized before everyprocedure, or synchronized whenever time settings on the ultrasoundprobe are changed or intermittently, as desired. Alternatively, theframe and line triggers that are derived from clock 208 can betransmitted to the medical device and used to synchronize clock 308. Aone-time constant synchronization may be sufficient in many cases,depending on the quality of the clocks and time duration of medicaldevice use.

In the present embodiment, the beamformer 210 provides frame and linetrigger signals. Every time a frame trigger signal or a line trigger israised, it is transmitted from the console/control unit (e.g., controlunit 201) via the wireless transceiver (e.g., wireless transceiver 209)to the medical device 300. Alternatively one could also transmit onlythe frame triggers or a predetermined subset (e.g., odd, even, everyfifth, etc.) of the line triggers. Both the medical device 300 and theconsole/control unit store the clock time of the respective triggersignals.

When the processor 306 on the medical device 300 detects a relevantsignal from the sensor 302, it parses the signal, making it ready fortransmission. The processor 306 is adapted to assign a time of receptionof the signal from the sensor 302 that is stored in the memory 307. Themedical device then transmits the signal data and the time of the sensorsignal to the console/control unit wirelessly (i.e., via the wirelesstransceiver 312 and the wireless transceiver 209). So, in the presentrepresentative embodiment, the sensor signal having a peak magnitude attime Δt relative to line trigger n+1 is transmitted from the medicaldevice 300 to the console/control unit, where its processor (e.g.,processor 205) using instructions from the memory 206 determines thelocation of the sensor relative to the image of the first frame.

As can be appreciated, because the timing of the frame and line triggersare transmitted by a clock synchronized to the clock 308, by measuringthe time of receipt of the signal from the sensor (likely the time ofits peak magnitude), the location of the sensor 302 relative to thelocation of transducers of the array (and thus the frame image) can bedetermined by straight forward velocity/time calculations. In thepresent representative embodiment, the x,y coordinates of the sensor 302(or x,y,z coordinates for volumetric imaging) are known relative to then+1 transducer, the location of which is mapped to a coordinate systemof the resultant first frame image. As such, the processor of theconsole/control unit determines the position of the sensor 302, andsuperposes the position on the frame image by executing instructionsstored in the memory.

As noted above, processor 306 can be configured to transmit varyingtypes of signal; namely the whole RF sensor frame, a clipped portion ofthe data, or a computed location of the sensor. Any combination of theabove is also possible.

In the latter embodiment, the frame and line trigger signals areprovided to the medical device for storage in the memory 307. In thisrepresentative embodiment, the memory 307 stores instructions executedby the processor to determine the location of the sensor 302 relative tothe frame and line triggers. The data for the location of the sensor 302are then transmitted (again, wirelessly) to the console/control unit sothe location can be superposed on the particular frame image in realtime.

An interventional medical device, such as a needle, an endoscope orendoscopic instrument, may be used to operate an end-effector in aninternally situated area of interest of an object, such as a patient. Asdiscussed above, it is possible to identify and track the medical deviceusing ultrasound-guided procedures by attaching a miniaturizedultrasound sensor to the medical device, and analyzing the ultrasounddata received by the sensor as the imaging probe insonifies the medium.For example, the ultrasound sensor may be located at or near a distalend (e.g., the tip) of the medical device, and thus be used to identifythe precise localization of the distal end, which is desirable in manyapplications.

Generally, according to various embodiments, the sensor for tracking theposition of the interventional medical device may be passive or active.This may be accomplished by detecting an ultrasonic wave impinging onthe sensor, which is attached to the interventional medical device, andwirelessly transmitting information about this acoustic event to theconsole (e.g., wireless transceiver 209 of control unit 201) of theimaging system. Generally, passive sensors convert received ultrasonicsignals into corresponding electrical signals, which are detected byexternal receivers, such as the wireless transceiver 209 of the controlunit 201 in FIG. 2 . Active ultrasound sensors likewise convert receivedultrasonic signals into corresponding electrical signals, but then takeactive steps to transmit the electrical signals to external receivers,such as the wireless transceiver 209 or a receiver located in the handleor hub of the medical device to which the sensor is attached, such aswireless transceiver 312 in hub 304 in FIG. 3 (via electrical or opticalconductors 303 or via a medical device wireless transceiver (notshown)). Notably, in an embodiment, the wireless transceiver 312 may beused as the receiver receiving RF signals from the passive ultrasoundsensor, as well.

In an embodiment including a passive sensor attached to theinterventional medical instrument, energy in ultrasonic waves (acousticpulse) hitting an ultrasound transducer is harvested, and the harvestedenergy is used to enable transmission of a corresponding RF signal (RFpulse) to an external receiver. The RF signal contains information ofthe acoustic event (i.e., conversion of an acoustic wave to acorresponding RF signal).

FIG. 5 is a conceptual diagram depicting an ultrasound transducer in apassive sensor that harvests energy, according to a representativeembodiment. Referring to FIG. 5 , sensor 500 comprises a small radiofrequency identification (RFID) chip 510 and antennae 515. The sensor500 is shown attached to the medical device 214 for purposes ofillustration. Information is transmitted by the RFID chip 510 by to awireless receiver 501 via the antennae 515. In various configurations,the receiver 501 may be implemented as the wireless transceiver 209 inthe control unit 201. Conventionally, the transmitted information may bea stored bit sequence; however, in the depicted embodiment, the RFIDchip 510 transmits an RF signal (sensor signal) related to the state ofthe senor 500 (indicating an acoustic event) rather than a bit sequence.The sensor 500 in this case may be a structure that converts an incomingacoustic wave into a surface acoustic wave entering the RFID chip 510,as discussed below.

More particularly, the ultrasound imaging probe 211 transmits ultrasonicwaves (acoustic pulses) 540 that are received by the RFID chip 510, andthe energy in the ultrasound waves 540 is harvested to power the RFIDchip 510. The RFID chip 510 then transmits the RF signal related to thestate of the sensor 500 to the receiver 501. The timing of when theultrasonic waves 540 hit the RFID chip 510 (and are transformed tocorresponding RF signals) is known. Accordingly, the location of theRFID chip 510, and thus the location of the sensor 500, may bedetermined within the area of interest of the object (e.g., by theprocessor 205 executing a signal processing algorithm) based on delaybetween an ultrasonic wave hitting the RFID chip 510 and receipt of thecorresponding RF signal. In other words, the location of the sensor 500is determined based on a known delay between the ultrasonic waves 540hitting the sensor 500 and the receiver 501 receiving the correspondingelectrical signal, as well as known information about a transmit patternof the ultrasound imaging probe 211.

In the depicted embodiment, the RFID chip 510 includes a surfaceacoustic wave (SAW) resonator 520 and a transition area 530. The SAWresonator 520 is an electronic resonator circuit tuned to a specificresonance frequency for converting ultrasonic waves to electrical RFsignals, enabling the SAW resonator 520 to harvest the energy from theultrasonic waves 540 that match the resonance frequency. The SAWresonator 520 also converts the ultrasonic waves 540 to corresponding RFsignals that are transmitted to or otherwise detected by the receiver501. That is, the energy in the ultrasonic waves 540 hitting theultrasound sensor 500 is harvested, and used to transmit RF signals,converted by the SAW resonator 520 and containing information of theacoustic event, to the receiver 501.

The transition area 530 of the RFID chip 510 performs mode conversion,transforming the longitudinal ultrasonic waves 540 (acoustic pulses),e.g., received from the ultrasound imaging probe 211, to correspondingsurface acoustic waves that resonate the SAW resonator 520. This modeconversion occurs when the ultrasound energy impacts a surface of theinterface area at an angle steeper than a certain critical angle, aswould be apparent to one skilled in the art. As the SAW resonator 520,along with the transition area 530, may be a foil-like structure, it canbe shaped such that the transition area 530 is oriented appropriatelyrelative to the impinging ultrasonic waves 540 for mode conversion tosurface acoustic waves to occur. Generally, mode conversion occurs whenthe ultrasonic waves encounter an interface between materials ofdifferent acoustic impedances, and the incident angle is not normal tothe interface.

The SAW resonator 520 includes a piezoelectric layer 521 formed over asubstrate (not shown), and an electrode layers 522 and 523 formed overthe piezoelectric layer 521. The piezoelectric layer may be formed ofany compatible piezoelectric material, such as lithium niobate (LiNbO₃)or aluminum nitride (AlN), and the electrode layer 522 may be formed ofany compatible electrically conductive material, such as molybdenum (Mo)or tungsten (W), for example. In the depicted embodiment, the SAWresonator 520 is an Inter-Digital Transducer (IDT), in which theelectrode layers 522 and 523 have an interleaving comb-like structure.The antennae 515 are attached to the IDT for transmission of the RFsignals. Thus, the SAW resonator 520 converts the incident surfaceacoustic waves propagated from the transition area 530 into RF signalsthat are collected and transmitted to the receiver 501.

In another embodiment including a passive sensor, an external RF signalis continuously broadcast by an RF transmitter from an external antenna(or at least continuously broadcast over timespans where responses areexpected based on previously detected sensor location.) The sensorincludes an electronic resonator circuit tuned to the frequency of theexternal RF signal. The electronic resonator circuit has a local antennaand an ultrasound transducer with a resonance frequency, where theultrasound transducer is capable of modulating and/or detuning theelectronic resonator circuit in response to receiving the ultrasonicwaves from the ultrasound imaging probe 211. When the electronicresonator circuit is within the nearfield of the external antenna (e.g.,less than one tenth of the wavelength of the RF signal), it presents amodulated load to the external antenna, indicating when the ultrasoundtransducer converts an ultrasonic wave to a corresponding electrical RFsignal. This modulated load on the external antenna can be detected bymonitoring power levels going into the external antenna. For example, anincrease in current drawn by the external antenna may indicate thepresence of the modulated load resulting from resonation of theultrasound transducer, although other indications may be used withoutdeparting from the scope of the present teachings. This embodiment maybe based on a modification of passive RFID chips and/or capacitivemicromachined ultrasonic transducer (CMUT) devices operating in thelower RF ranges, which may be any RF signal with frequency less thanabout 100 MHz (e.g., 120 kHz-150 kHz or 13.56 MHz). The nearfield for100 MHz would be about 30 cm, for example.

FIGS. 6A and 6B are conceptual diagrams depicting a passive sensor thatreceives continuously broadcast external RF signal from an RFtransmitter 650 (sometimes referred to as external transmitter 650) viaan external antenna 651 remote from the medical device 214, according toa representative embodiment. The RF transmitter 650 may be included inthe control unit 201 or the hub 304, for example, or may be a separatedevice.

Referring to FIG. 6A, passive sensor 600 comprises an electronicresonator circuit 610 tuned to the frequency of the external RF signalfrom the external antenna 651, and includes a capacitive element 612(i.e., an ultrasound transducer), and an antenna 615 (sometimes referredto as local antenna 615) attached to the interventional medical device214. Alternatively, the interventional medical device 214 may be used asthe antenna (eliminating the need for the antenna 615), and the RFtransmitter 650 could still be used to detect modulated load when placedat a sub-wavelength, nearfield distance, as discussed above. Thecapacitive element 612 in the electronic resonator circuit 610 may be apassive CMUT device or CMUT-like device, for example, as shown in FIG.6B. A CMUT is an ultrasound transducer in which the energy transductionbetween acoustic and electrical signals occurs due to change incapacitance. It is understood that a CMUT-like device has a capacitancethat changes slightly according to pressure from an acoustic wavehitting it. The capacitive element 612 is able to sense the ultrasonicwaves 640, and modulates and/or detunes the electronic resonator circuit610 in response. That is, the ultrasound sensor 600 is basically acapacitive micromachined microphone for ultrasound frequencies. Thecapacitive element 612 is modulated by the ultrasonic waves 640 from theultrasound imaging probe 211. The membranes in a CMUT-like device can beimplanted with charge so they attract each other and make the capacitivemodulation due to ultrasound more pronounced.

FIG. 6B is a simplified cross-sectional view of an illustrative CMUT620, which may be incorporated as the capacitive element 612 in theelectronic resonator circuit 610 of FIG. 6A, providing a CMUT-likedevice. The CMUT 620 includes substrate 621 forming a cavity 622. Activeelectrode 623 is formed at the bottom of the cavity 622, and groundelectrode 624 is formed on an upper surface of the substrate 621 around(or on either side of) the cavity 622. A vibrating membrane 625 isconnected to the ground electrode 624 across the cavity 622, enablingthe vibrating membrane 625 to oscillate in response to receivedultrasonic waves 640. Generally, a bias voltage is applied over theactive and ground electrodes 623 and 624, respectively, and theoscillation of the vibrating membrane 625 converts the ultrasonic waves640 to an electrical RF current signal output at the activatingelectrode 623. However, in the present embodiment, the bias voltage isnot needed, and the signal may consist of a change in capacitanceleading to a change in the resonance frequency of passive sensor 600 asdetected by RF transmitter 650.

Continuous transmission of lower frequency RF signals (e.g., less thanabout 100 MHz) from the RF transmitter 650 may be performed at fixedfrequency to which the frequency of the electronic resonator circuit 610is initially tuned. The RF transmitter 650 is thus able to detectloading of the external antenna 651 caused by the modulation loadingand/or detuning of the electronic resonator circuit 610 in response tothe ultrasound sensor 600 receiving ultrasonic waves 640 from theultrasound imaging probe 211. Because the measurement of the modulationsignal is performed at the RF transmitter 650 side (based on detectionof antenna loading), there is no need to receive and/or processreflected or transmitted RF signals from the ultrasound sensor 600.Thus, transmission of the RF signal from the external antenna 651 neednot be interrupted for receiving RF signals, and so the modulation canbe measured continuously. Accordingly, the location of the passivesensor 600 within the area of interest of the object may be determined(e.g., by the processor 205 executing a signal processing algorithm)based on delay between an ultrasonic wave hitting the electronicresonator circuit 610 and detection of loading of the external antenna651.

In another embodiment including a passive sensor, an external RF signalis continuously broadcast by an RF transmitter from an external antenna,as mentioned above, where the external antenna is remote from thepassive sensor. The passive sensor includes an electronic resonatorcircuit tuned to the frequency of the external RF signal. The electronicresonator circuit has an attached local antenna, and includes anultrasound transducer (ultrasound sensor) having a resonate cavity thatmodulates and/or detunes the electronic resonator circuit whenresonating at its resonance frequency in response to received ultrasonicwaves.

The electronic resonator circuit is configured in combination with thelocal antenna, such that a reflection signal of the illuminatingexternal RF signal is created at a frequency of a higher harmonic.Therefore, the higher harmonic reflection signal may be detected usingan external RF receiver. Thus, transmission of the external RF signalfrom the external antenna need not be interrupted to receive thereflection signal, and so modulation of the passive sensor can bemeasured continuously. When ultrasonic waves hitting the sensor changethe capacitance, the resonating circuit detunes, and thus the amplitudeof resonance due the continuous broadcasting RF transmitter reduces.This, in turn, also reduces the reflected harmonic signal that iscontinuously received, i.e. the ultrasound modulation of the capacitiveelement leads to an amplitude modulation of the received harmonicreflection. The electronic resonator circuit works in the farfield ofthe external antenna (e.g., greater than one tenth of the wavelength ofthe RF signal), and at a frequency significantly higher that theultrasound frequency of the imaging probe.

More particularly, FIG. 6C is a conceptual diagram depicting a passivesensor that receives continuously broadcast external RF signal at firstfundamental frequency F1, and reflects a harmonic signal at secondfundamental frequency F2, according to a representative embodiment.

Referring to FIG. 6C, passive sensor 600′ comprises electronic resonatorcircuit 610, which includes a capacitive element 612 (i.e., anultrasound transducer) and receive local antenna 615 and transmit localantenna 617. The electronic resonator circuit 610 is tuned to receivethe RF signal from the RF transmitter 650 and transmitter antenna 651 atthe first fundamental frequency F1, via the receive local antenna 615,and to transmit the harmonic reflection RF signal to the receiverantenna 661 and RF receiver 960 at the second fundamental frequency F2,via the transmit local antenna 617. The RF transmitter 650 and/or the RFreceiver 660 may be included in the control unit 201 or the hub 304, forexample, or may be separate devices. As stated above, the harmonicreflection signal of the RF signal is created at a higher harmonicfrequency, such that the second fundamental frequency F2 is greater thanthe first fundamental frequency F1. Therefore, the higher harmonicreflection signal may be detected by the external RF receiver 660. Thus,transmission of the RF signal from the external RF transmitter 650 neednot be interrupted for reception of the harmonic reflection signal, andmodulation of the passive sensor 600′ can be measured continuously.

In contrast to the passive sensors, discussed above, the wirelessultrasound sensor may be an active sensor. In an embodiment including anactive sensor attached to the interventional medical instrument, energyin ultrasonic waves (acoustic pulse) hitting an ultrasound transducer isharvested, as discussed above with reference to FIG. 5 , and theharvested energy is used to transmit an electrical RF signal, containinginformation of the acoustic event, to an active (e.g., battery powered)circuit in or near the handle or hub (such as hub 304) of theinterventional medical device. The battery powered active circuit mayinclude a receiver, an amplifier and a transmitter, for example. Thus,the active circuit is able to amplify the received RF signal, which isused to modulate a high frequency RF signal transmitted from the hub orhandle of the medical device to the control unit 201 (e.g., via thewireless transceiver 209).

FIG. 7 is a conceptual diagram depicting an ultrasound transducer in anactive sensor that harvests energy to send an RF signal for activeretransmission, according to a representative embodiment. Referring toFIG. 7 , sensor 700 includes some of the same components as in sensor500, discussed above with reference to FIG. 5 , in which case the samereference numerals are used. The sensor 700 comprises a small RFID chip510 and antennae 515. The sensor 700 is shown attached to the medicaldevice 214 for purposes of illustration. Information is transmitted bythe RFID chip 510 to a wireless receiver 701 in active circuit 710(e.g., repeater) via the antennae 515, where the active circuit 710 islocated in the handle or hub 304 of the medical device 300 (although notshown in FIG. 3 ). The active circuit 710 also may include an amplifier702 for amplifying the received RF signal and a transmitter 703 forwirelessly transmitting the amplified RF signal to the wirelesstransceiver 209 in the control unit 201. The active circuit 710efficiently transmits the RF signal (data) it receives from the sensor700 to the control unit 201. Since the active circuit 710 has an activepower source, e.g., battery 711, it can operate at high frequencies(e.g., greater than about 200 MHz) to maximize antenna efficiency. Ofcourse, other means of providing power to the active circuit 710 may beincorporated without departing from the scope of the present teachings.

In an embodiment, the received RF signal may be provided from thereceiver 701 to the signal conditioning module 305, which includes theamplifier 309, filter 310, and digitizer 311, before being provided tothe transmitter 703 for wireless transmission. In this case, thefunctionality of the amplifier 702 may be replaced by that of theamplifier 309 in the signal conditioning module 305. In anotherembodiment, the receiver 701 and the transmitter 703 may be replaced bya transceiver that receives at a lower and transmits at a higherfrequency. In sum, the RFID chip 510, powered by harvested energy,transmits an RF signal related to the state of the sensor 700(indicating an acoustic event). This RF signal is received, amplifiedand retransmitted by the active circuit 710 (effectively acting as arepeater) to the control unit 201.

As discussed above, the ultrasound imaging probe 211 transmitsultrasonic waves (acoustic pulses) 540 that are received by the RFIDchip 510, and the energy in the ultrasonic waves 540 is harvested topower the RFID chip 510. The RFID chip 510 then transmits the RF signalrelated to the state of the sensor 700 to the active circuit 710, foramplification and transmission to the control unit 201. The timing ofwhen the ultrasonic waves 540 hit the RFID chip 510 (and are transformedto corresponding RF signals) is known. Accordingly, the location of theRFID chip 510, and thus the location of the sensor 700, may bedetermined within the area of interest of the object (e.g., by theprocessor 205 executing a signal processing algorithm) based on delaybetween an ultrasonic wave hitting the RFID chip 510 and receipt of thecorresponding RF signal. In other words, the location of the sensor 700is determined based on a known delay between the ultrasonic waves 540hitting the sensor 700 and the receiver 701 receiving the correspondingelectrical signal, as well as known information about a transmit patternof the ultrasound imaging probe 211. It is understood that the otherpassive sensors discussed above, e.g., including passive sensor 600 inFIGS. 6A and 6B, may be incorporated in place of the sensor 700 in thedepicted embodiment, without departing from the scope of the presentteachings.

If the interventional medical device 214 is a needle, for example, aSAW-based sensor, such as sensor 500 or 700, may be located near the tipof the needle, and the needle itself may be used as the antenna (e.g.,instead of antennae 515). The wireless receiver 701 may be in direct orclose contact to the needle at the proximal end to pick up the sensorsignal efficiently. The received data can be used to modulate an RF waveof much higher frequency than the sensor signal (to allow sufficientmodulation depth to capture the bandwidth of the sensor signal). Thishigh frequency RF signal can then be amplified by the amplifier 702 andefficiently transmitted wirelessly by the transmitter 703 using asmaller antenna (due to the high frequency).

An advantage of the receiver 701 being in close contact, as opposed todirect contact, with the needle is that no on-needle interconnect isneeded. However, the increased range and sensitivity provided by anactive RF transmitter (transmitter 703) can still be leveraged. Also,because the receiver 701 and the active transmitter 703 do not have tobe in direct contact with the medical device 214, but merely in closeproximity, the active circuit 710 is easier to provide as a separatenon-disposable part. For example, the hub may be reusable, such that thehub clips onto the end of a needle. Because the communication with thesensor 700 via the needle is wireless, there is no electrical connectorrequired, thereby decreasing disposable device cost and reliabilityissues. In an embodiment, the reusable hub may be made in a patchform-factor, for example, that can be adhered to the surface of theobject (e.g., the skin of the patient) close to the region of interest.

Also, the bandwidth of the sensor signal from the sensor 700 can bereduced using an envelope detector (not shown), for example. Anillustrative analog manner for implementing the envelope detector is touse an analog multiplier to square the sensor signal. This createsfrequency shifted components near DC and double the carrier frequency. Alow pass filter isolates the low frequency components representing acrude envelope detector, to provide a signal with much lower bandwidth.

In another embodiment including an active wireless sensor, the sensor oninterventional medical device may be connected by wires to an activecircuit in the hub and/or handle of the medical device. The activecircuit is optimized to efficiently extract data from the sensor, andthe received signal may be used to modulate a high frequency RF signaltransmitted from the hub and/or handle to the control unit 201 of theconsole.

FIG. 8 is a conceptual diagram depicting an ultrasound transducer in anactive sensor that sends an RF signal for retransmission via wires,according to a representative embodiment. Referring to FIG. 8 , some ofthe components are the same as those in FIG. 7 , discussed above, inwhich case the same reference numerals are used. In this embodiment, themedical device 214 may be needle shaped, or otherwise elongated, withultrasound sensor 800 located near the tip. The ultrasound sensor 800 isconnected to active electronics, such as the active circuit 710′,through one or more miniature wires 815 running along the needle-likemedical device 214. The miniature wires 815 may run internally orexternally along the medical device 214, without departing from thescope of the present teachings. The active circuit 710′ is located inthe handle or hub 304 of the medical device (although not shown in FIG.3 ). The active circuit 710′ includes amplifier 702 for amplifying thereceived RF signal and a transmitter 703 for wirelessly transmitting theamplified RF signal to the wireless transceiver 209 in the control unit201. No wireless receiver 701 is needed. To reduce the bandwidth of theRF signal that is transmitted by transmitter 703, an analog envelopedetection may be performed e.g., by amplifier 702 as described above.When the ultrasound sensor 800 is small, it may have low sensitivity andproduce a signal that is easily corrupted by transfer over theinterconnect (including wire(s) 815) of the medical device 214. Thus,care must be taken on how to robustly extract the RF signal from thesensor through the medical device 214 interconnect (e.g., needleinterconnect), and active electronics offers opportunity to do so.

For example, assuming for purposes of discussion that the ultrasoundsensor 800 functions like a miniature condenser microphone that has avarying capacitance as the ultrasonic wave perturbs its membrane, asdiscussed above with reference to FIGS. 6A and 6B, for example. In thiscase, the ultrasound sensor 800 may be made part of an electronicresonator circuit that FM modulates a high frequency oscillation. Thissignal is then amplified (e.g., by the amplifier 702) and directlytransmitted (e.g., by the transmitter 703) via the miniature antenna inthe handle or hub (e.g., hub 304).

If the ultrasound sensor 800 is polyvinylidene fluoride (PVDF) based,for example, it can not drive a capacitive load. In this case, theactive electronics in the hub will function as a charge amplifier. Thiskeeps the voltage over the interconnect constant to eliminate parasiticinterconnect capacitance influence, while measuring the sensor currentsthat the acoustic signal generates. Once the sensor signal isefficiently extracted in the hub, the power source in the hub (e.g.,battery 711) can be leveraged to create a strong wireless transmissionthat uses higher frequencies, enabling the use of small footprintantennas with high efficiency.

Other variations to the disclosed embodiments can be understood andeffected by those skilled in the art in practicing the claimedinvention, from a study of the drawings, the disclosure, and theappended claims. In the claims, the word “comprising” does not excludeother elements or steps, and the indefinite article “a” or “an” does notexclude a plurality. A single processor or other unit may fulfill thefunctions of several items recited in the claims. The mere fact thatcertain measures are recited in mutually different dependent claims doesnot indicate that a combination of these measured cannot be used toadvantage. A computer program may be stored/distributed on a suitablemedium, such as an optical storage medium or a solid-state mediumsupplied together with or as part of other hardware, but may also bedistributed in other forms, such as via the Internet or other wired orwireless telecommunication systems. Any reference signs in the claimsshould not be construed as limiting the scope.

1. A system for performing a medical procedure in a region of interestof a patient, the system comprising: an interventional device insertableinto the region of interest; a passive sensor attached to a portion ofthe interventional device, the passive sensor configured to convert anultrasonic wave from an ultrasound imaging probe to a correspondingelectrical radio frequency (RF) signal; an RF transmitter configured to:continuously broadcast, via an external antenna remote from the passivesensor, an external RF signal that is received by the passive sensor,and detect, on the external antenna, a modulated load indicating whenthe passive sensor converted the ultrasonic wave to the correspondingelectrical RF signal; and a processor configured to determine a locationof the passive sensor within the region of interest based on detectionof the modulated load on the external antenna by the RF transmitter. 2.The system of claim 1, wherein the location of the passive sensor isdetermined based on (i) delay between receipt of the ultrasonic wave atthe passive sensor and the detection of the modulated load on theexternal antenna and (ii) information about a transmit pattern of theultrasound imaging probe.
 3. The system of claim 1, wherein the passivesensor is configured to reflect the broadcasted external RF signalreceived by the passive sensor, wherein the reflected signal istransmitted at a higher harmonic than the broadcasted external RFsignal.
 4. The system of claim 1, wherein the passive sensor comprisesan electronic resonator circuit attached to a local antenna, theelectronic resonator circuit tuned to a frequency of the external RFsignal, and the passive sensor configured to modulate the electronicresonator circuit in response to receipt of the ultrasonic wave togenerate the modulated load detected on the external antenna of the RFtransmitter.
 5. The system of claim 4, wherein the passive sensor has aresonate cavity that modules the electronic resonator circuit inresponse to receipt of the ultrasonic wave.
 6. The system of claim 4,wherein the electronic resonator circuit includes a capacitive elementconfigured to sense the ultrasonic wave and generate an amplitudemodulation based on the broadcasted external RF signal.
 7. The system ofclaim 1, wherein the RF transmitter detects the modulated load based onmonitoring power levels going into the external antenna.
 8. The systemof claim 1, further comprising the ultrasound imaging probe configuredto transmit the ultrasonic wave received and converted by the passivesensor.
 9. A method for performing a medical procedure in a region ofinterest of a patient, the method comprising: converting, by a passivesensor attached to a portion of an interventional device, an ultrasonicwave from an ultrasound imaging probe to a corresponding electricalradio frequency (RF) signal; continuously broadcasting, via an externalantenna remote from the passive sensor, an external RF signal that isreceived by the passive sensor; detecting, on the external antenna, amodulated load indicating when the passive sensor converted theultrasonic wave to the corresponding electrical RF signal; anddetermining a location of the passive sensor within the region ofinterest based on detection of modulated load on the external antenna.10. The method of claim 9, wherein the location of the passive sensor isdetermined based on (i) delay between receipt of the ultrasonic wave atthe passive sensor and the detection of the modulated load on theexternal antenna and (ii) information about a transmit pattern of theultrasound imaging probe.
 11. The method of claim 9, further comprising:reflecting the broadcasted external RF signal received by the passivesensor, wherein the reflected signal is transmitted at a higher harmonicthan the broadcasted external RF signal.
 12. The method of claim 9,wherein the passive sensor comprises an electronic resonator circuitattached to a local antenna, the method further comprising: tuning theelectronic resonator circuit to a frequency of the external RF signal;and modulating the electronic resonator circuit in response to receiptof the ultrasonic wave to generate the modulated load detected on theexternal antenna of the RF transmitter.
 13. The method of claim 12,wherein the passive sensor has a resonate cavity that modules theelectronic resonator circuit in response to receipt of the ultrasonicwave.
 14. The method of claim 9, further comprising monitoring powerlevels going into the external antenna to detect the modulated load. 15.The method of claim 12, wherein the electronic resonator circuitincludes a capacitive element and the method further comprisesgenerating, using the capacitive element, an amplitude modulation of thebroadcasted external RF signal.
 16. A non-transitory computer-readablestorage medium having stored a computer program comprising instructions,which, when executed by at least one processor, cause the processor tocontinuously broadcasting, via an external antenna remote from a passivesensor attached to a portion of an interventional device, an external RFsignal that is received by the passive sensor, wherein the passivesensor converts an ultrasonic wave from an ultrasound imaging probe to acorresponding electrical radio frequency (RF) signal; detecting, on theexternal antenna, a modulated load indicating when the passive sensorconverted the ultrasonic wave to the corresponding electrical RF signal;and determining a location of the passive sensor within the region ofinterest based on the detected modulated load.
 17. The non-transitorycomputer-readable storage medium of claim 16, wherein the location ofthe passive sensor is determined based on (i) delay between receipt ofthe ultrasonic wave at the passive sensor and detection of the modulatedload on the external antenna and (ii) information about a transmitpattern of the ultrasound imaging probe.
 18. The non-transitorycomputer-readable storage medium of claim 16, wherein the passive sensorcomprises an electronic resonator circuit attached to a local antenna,the electronic resonator circuit tuned to a frequency of the external RFsignal, and the passive sensor configured to modulate the electronicresonator circuit in response to receipt of the ultrasonic wave togenerate the modulated load detected on the external antenna of the RFtransmitter.
 19. The non-transitory computer-readable storage medium ofclaim 18, wherein the passive sensor has a resonate cavity that modulesthe electronic resonator circuit in response to receipt of theultrasonic wave.
 20. The non-transitory computer-readable storage mediumof claim 16, the instructions, when executed by the processor, furthercause the processor to monitor power levels going into the externalantenna to detect the modulated load.